Highly Dispersed Blast-Furnace Sludge as a New Micronutrient Fertilizer: Promising Results on Rapeseed

Due to the growing population of Earth, the problem of providing food comes to the fore. Therefore, the search for new, economically available sources of trace elements for crop production is relevant. One of these potential sources is blast-furnace sludge: highly dispersed metallurgical waste, the industrial processing of which is difficult due to its high zinc content. We studied the effect of blast-furnace sludge on rapeseed plants in laboratory, greenhouse, and field experiments and also assessed the accumulation of sludge components in plant organs. The studied sludge sample consisted of micron and submicron particles containing compounds of iron, silicon, aluminum, zinc, calcium, and sulfur. Used concentrations: laboratory—0.01, 0.1, 1%, 10, and 100 g L−1; greenhouse—0.01, 0.1, 1, 10, and 100 g kg−1; field—0.5, 2, and 4 t ha−1. During a laboratory experiment, a decrease in the germination of rapeseed seeds exposed to 0.01, 0.1, 10, and 100 g L−1 waste was observed, but 1 g L−1 promoted the increase of this indicator by 7% regarding control (0 g L−1). While inhibiting seed germination, the sludge had a beneficial effect on the vegetative performance of plants. Reverse effects were noted in the greenhouse experiment as an increase in seed germination (introduction of 1 g kg−1 of sludge to the substrate caused maximum stimulation) and a decrease in rapeseed morphometric parameters were observed. However, at a concentration of 10 g kg−1, the root mass increased by 43% and the stem mass by 63%. In the same group, the highest content of chlorophylls was noted. The number of pods in all experimental groups of plants was less than in control (0 g kg−1) plants, but at the same time, in the variants of 0.01 and 1 g kg−1, the weight of seeds was noticeably increased, by 15.6 and 50%, respectively. Under the conditions of the field experiment, the sludge had a positive effect on the indicators of biological and economic productivity. Thus, exposure to 0.5 and 2 t ha−1 of sludge significantly increased the dry matter and leaf area. The highest values of photosynthetic capacity were recorded at a dose of 2 t ha−1. The maximum increase in yield was ensured by the introduction of sludge at a concentration of 0.5 and 2 t ha−1. The sludge dose of 4 t ha−1, which was also used, either had no effect or suppressed the development of the analyzed traits. The study of the accumulation of zinc and iron in the organs of plants showed the absence of a pronounced dose-dependent accumulation of zinc in the organs of rapeseed, while for iron, an increase in the content of the element in the organs of plants associated with an increase in the concentration of sludge in the soil was recorded. Our results demonstrate the promise of further research and development of methods for the agricultural use of highly dispersed sludge from wet gas cleaning of blast furnace production